This invention relates to a fuel feed apparatus which feeds fuel to an internal combustion engine, and more particularly, to a fuel feed apparatus which is capable of promoting atomization of the fuel by supplying assist air to a fuel injection valve disposed in an intake passage of the internal combustion engine and serving to inject the fuel.
Heretofore, an internal combustion engine of the type that one cylinder is provided with a plurality of intake valves has been put into practice widely.
Further, there has been well known a fuel injection valve of the type that a plurality of fuel injection nozzles are directed to a plurality of intake valves individually so as to inject the fuel toward the intake valves to thereby reduce fuel adhesion to the intake passage and hence improve the performance of the engine.
In addition, there has been well known such a technique named air assist that air is injected from the fuel injection valve together with the fuel. For example, as disclosed in Japanese Utility Model Examined Publication No. 2-16057, it has been known as well that assist air is supplied to a fuel injection valve having two fuel injection nozzles so as to atomize the fuel sprayed for two intake valves by the assist air. Moreover, in the fuel injection valve disclosed in Japanese Patent Unexamined Publication No. 64-24161 as well, assist air is supplied to the fuel injection valve having two fuel nozzles so as to atomize the fuel sprayed for two intake valves by the assist air.
According to these air assist techniques, since the fuel can be atomized by the assist air, combustion can be improved and hence the constituents of exhaust gas can be improved. Still furthermore, Japanese Patent Unexamined Publication No. 63-314363 discloses a technique that a sleeve to be provided at the tip end of the fuel injection valve is divided into two parts so as to form assist air passages in abutting surfaces of the two sleeve members.
According to the conventional air assist technique described above, the assist air is supplied to two sprays of fuel directed to two intake valves individually so as to form two separate sprays of fuel atomized by the assist air. However, in case of atomizing the fuel due to air assist, since the assist air is made to collide against the sprayed fuel, as the particle size of the air-assisted sprayed fuel becomes smaller to promote the atomization, the spray cone angle of the air-assisted sprayed fuel becomes larger. For this reason, if it is intended to form two air-assisted sprays as in the conventional air assist technique, it is necessary to make small the spray cone angle of each spray, resulting in the problem that the atomization cannot be performed satisfactorily.
In consequence, according to the conventional air assist technique, it is impossible to perform the atomization satisfactorily, resulting in the problem that the fuel adheres to the intake passage or the intake valves.
Particularly when it is required to inject a large amount of fuel such as when the internal combustion engine is operated in high-load condition or operated at low temperatures immediately after the engine is started, the fuel injection time of the fuel injection valve is prolonged in order to increase the fuel injection amount so that the fuel injection is started before the intake valves are opened in some cases. If the fuel is injected at the time when the intake air flows slow, such as before the intake valves are opened, according to the conventional air assist technique, a large amount of fuel adheres to the intake passages or the intake valves, thereby making it impossible to improve the combustion in the cylinder sufficiently and hence to improve the constituents of the exhaust gas satisfactorily.
Further, according to the conventional air assist technique, forming of the assist air passages requires drilling of elongated holes, resulting in the problem that the manufacturing cost is increased. To cope with this, it is considered to form the assist air passages between the two members. However, in case that the two members are plasticized, there is a possibility that, in joining the two members to each other, the assist air passages are deformed due to crushing of the bonding agent, resin or the like to thereby cause the clogging of the assist air passages or the lack of assist air flow.